Turbine engines, and particularly gas turbine engines, also known as combustion turbine engines, are rotary engines that extract energy from a flow of combusted gases passing through the engine onto a multitude of turbine blades. Gas turbine engines have been used for land and nautical locomotion and power generation, but are most commonly used for aeronautical applications such as for airplanes, including helicopters. In airplanes, gas turbine engines are used for propulsion of the aircraft.
Gas turbine engines can have two or more spools, including a low pressure (LP) spool that provides a significant fraction of the overall propulsion system thrust, and a high pressure (HP) spool that drives one or more compressors and produces additional thrust by directing exhaust products in an aft direction. A triple spool gas turbine engine includes a third, intermediate pressure (IP) spool.
Gas turbine engines also usually power a number of different accessories such as generators, starter/generators, permanent magnet alternators (PMA), fuel pumps, and hydraulic pumps, e.g., equipment for functions needed on an aircraft other than propulsion. For example, contemporary aircraft need electrical power for avionics, motors, and other electric equipment. A generator coupled with a gas turbine engine will convert the mechanical power of the engine into electrical energy needed to power accessories.
Autotransformers (ATUs) are frequently used in power applications to interconnect systems operating at different voltage classes and to reduce the harmonic contents of the generators and the ripples at the outputs of the rectifiers. In aircrafts, autotransformers typically are used to step up or down voltages between generators and rectifiers. ATUs are separate from the generator, and add to the weight and volume of the engine. Furthermore, ATUs often require a forced liquid cooling system, which adds additional weight and volume to the engine.